The Short Message Service (SMS) is a text message received by a Mobile Station (MS) in 2G cellular system or User Equipment (UE) in 3G Cellular system or any terminal in a network capable of receiving a text message as specified in the SMPP protocol. An MS or UE can also generate the text message, which is known as mobile originated SMS. SMS Messages in the Cellular network are processed in the core network by an SMS center. The SMS center is responsible for processing incoming messages from Non-mobile (Cellular) entities know as External Short Message Entities (ESMEs), validating the subscriber and delivering the message to the mobile in the cellular network. If the MS or UE is not in the home network but is roaming in another cellular network which is known to the home network, and the MS or UE receives an SMS message, the SMS message is delivered to the MS or UE in the roaming network via an SS7 signaling network.
An (MS) or a UE in a 2.5G (such as GPRS network) or 3G such as a 3rd generation partnership project (3GPP) cellular system, which is running Internet Protocol-level (IP-level) applications, such as MobileIP, etc., has a need to send and/or receive IP-level signaling/control packets. Examples are Internet Control Message Protocol (ICMP) messages related to MobileIP protocol which, for example, are typically used to report a problem in the communication environment. These signaling/control IP packets are presently sent to, and received by, the MS over the air interface using transport/physical channels such as a dedicated channel (DCH), etc.
Hereinafter a UE, MS or a wireless transmit and/or receive unit (WTRU) shall be used interchangeably and includes but is not limited to a user equipment, mobile station, fixed or mobile subscriber unit, pager, or any other type of device capable of operating in a wireless environment. When referred to hereafter, a base station includes but is not limited to a base station, Node-B, site controller, access point or other interfacing device in a wireless environment.